Gas producing method

ABSTRACT

A method and apparatus for producing a gas well wherein gas is produced through a well bore and the well bore passes through a permafrost zone. The method and apparatus prevent solid hydrate from forming in the gas while passing through the permafrost zone toward the earth&#39;&#39;s surface.

United States Patent 72] Inventors Leland E. Wilson;

Jerry M. Trlckey, both of Anchorage, Alaska May 19, 1970 Dec. 14, 1971Atlantic Rlchfield Company New York, N.Y.

[21 Appl. No. [22] Filed [45] Patented [73] Assignee [54] GAS PRODUCINGMETHOD 9 Claims, 1 Drawlng Fig.

[52] U.S. Cl 166/302, 166/314, l66/D1G. 1

[51] Int. Cl EZlb 43/24 [50] Field of Search 166/302-304, 310, 57, 61,D16. 1, 314

[56] References Cited UNITED STATES PATENTS 3,207,219 9/1965 Mitchell1,012,777 12/1911 Wigle 166/61 735,449 8/1903 Berger 166/57 UX 2,614,63510/1952 Williams et a1. 166/303 X 2,914,124 11/1959 Ripley 4 166/573,348,614 10/1967 Sinclair eta1.. 166/310 3,393,733 7/1968 Kuo et a1.166/303 X 3,103,973 9/1963 Mullen 166/D1G. 1 OTHER REFERENCES Frlck,Thos. C. Petroleum Production Handbook, Vol. 11, NY. McGraw-Hill, 1962page 30- 32.

Primary Examiner-Stephen .l. Novosad A t!0rney.l Blucher S. Tharp andRoderick W. MacDonald ABSTRACT: A method and apparatus for producing agas well wherein gas is produced through a well bore and the well borepasses through a permafrost zone. The method and apparatus prevent solidhydrate from forming in the gas while passing through the permafrostzone toward the earth's surface.

Patented Dec. 14, 1971 AT IORNFY GAS PRODUCING METHOD BACKGROUND OF THEINVENTION Heretofore in the drilling of wells in the North Country whereeither continuous or discontinuous permafrost existed, it was thoughtthat the portion of the well bore which passed through the permafrostzone would have to be insulated, refrigerated, and the like.

This is generally true in the case of oil wells where thawing of thepermafrost is to be avoided, but it has now been found not to be asapplicable to gas wells.

SUMMARY OF THE INVENTION It has been found that natural gas or otherhydrocarboncontaining gas being produced through a well bore whichpasses through a permafrost zone can be sufficiently cooled whilepassing through the permafrost zone to cause the formation of a hydratewhich is a solid icelike material containing both water and hydrocarbonwhich can form at temperatures substantially above 32 F.

It has been found that this hydrate can be formed in the produced gas insuch quantity that plugging of the tubing through which the gas isproduced and/or pipes for carrying the gas over the earth's surface canoccur. The plugging is particularly troublesome wherever the flow pathof the gas has to change directions such as when passing through valves,Ts, and L's in the pipe system.

According to this invention there is provided a method for producing agas well through a permafrost zone and avoiding the problem of pluggingdue to hydrate formation in the produced gas by producing the gasthrough the well bore in a first conducting zone, heating the gas in thefirst conducting zone during at least part of the length of the wellbore, and controlling the heating step so that the gas is not cooledsufficiently while passing through the permafrost zone to cause theformation of substantial amounts of hydrate.

There is also provided according to this invention apparatus forproducing gas from a well in an area of permafrost utilizing a firstconduit means in the well bore for transmitting gas through the wellbore to the earth's surface, heater means for heating at least part ofthe first conduit means, and means for supplying energy to the heatermeans.

It is unusual to apply heat to a well bore which passes through apermafrost zone, but in the situation wherein a hydrocarbon-containinggas which also contains water is produced through a permafrost zone,controlled heating of that gas is generally necessary to preventsubstantial hydrate formation and to prevent hydrate plugging of theproduction tubing and/or surface piping associated with the well.

Accordingly, it is an object of this invention to provide a new andimproved method for producing a gas well in permafrost areas. it isanother object to provide a new and improved method for preventing theformation of solid hydrate when producing gas through a permafrost zone.It is another object to provide new and improved apparatus for gas wellproduction in a permafrost area. It is another object to provide new andimproved apparatus for the prevention of hydrate formation whileproducing a gas through a permafrost zone.

Other aspects, objects, and advantages of this invention will beapparent to those skilled in the art from this disclosure and theappended claims.

DETAILED DESCRIPTION OF THE INVENTION The drawing shows one apparatussetup employing this invention,

More particularly, the drawing shows a well bore 1 which can be linedwith conventional casing or not, as desired, and which is drilled in theearth 2 in a permafrost area so that well bore 1 penetrates a zone ofsurface tundra 3 which overlies a much thicker zone of permafrost 4.Under the permafrost layer is unfrozen rock and the like from which gasis produced in a conventional manner from formation 9. The well containsa surface wellhead 5 which contains a first conduit (first con ductingzone) 6, a second conduit (second conducting zone) 7, and a returnconduit or zone 8.

A gas, such as natural gas, other hydrocarbon-containing gas, carbondioxide, and the like, is produced from gas producing formation 9 intothe bottom 6 of conduit 6 up the well bore through permafrost zone 41into'the earths surface for further processing, use, and the like.

The gas passing from conduit 6 at the earth's surface normally passesthrough a piping system for further processing such as dehydration,sulfur and sulfur compound removal, and the like. Because of this, thegas passes through a large number of pipes and changes direction by wayof pipe T5 and L's a large number of times shortly after it leavesconduit 6.

Conduit 7 terminates in the well bore at a position above end 6' ofconduit 6 and preferably terminates in or near permafrost zone 4. Ends6' and 7 of conduits 6 and 7 are physically isolated from one another bya conventional single completion packer l0.

Conduit 8 has a conventional valve means 12 therein for regulating theflow of fluid from well bore 1 above packer l0 and into conventionalheater 13.

Heater 13 heats a fluid received from conduit 8 and passes the heatedfluid into conduit 14 by way of pump 15. From pump 15 the heated fluidpasses into conduit 7 and back down well bore 1.

In the apparatus of the drawing, at least part of the length of conduit6 in the permafrost zone 4 can be heated to above the temperature atwhich hydrate would form in the gas passing through conduit 6. Theheating is accomplished by way of a heated fluid emitting from end 7' ofconduit 7. The heated fluid contacts at least part of conduit 6 as itrises toward the earths surface for removal from well bore 1 by way ofconduit 8.

The length of conduit 7 can vary widely so that end 7 can emit theheated fluid therefrom at a point below the lowest level of permafrostzone 4, at about the lowest level of permafrost zone 4, above the lowestlevel of permafrost zone 4, and any desired combination thereof so longas the gas passing through conduit 6 is sufficiently heated so thathydrate does not form in the gas as it passes through permafrost zone 4.

Conduit 7 can also be employed concentrically with respect to conduit 6or either the interior or exterior or both of conduit 6. Thus, theheated fluid flows downwardly in inner and/or outer concentric contactwith conduit 6 and the fluid emitted from end 7' rises in the annulus ofthe well bore to the earths surface for removal through conduit 8.

The heating fluid employed could be gaseous or liquid but is preferablyliquid because of a liquids normally higher thermal capacity andconductivity. Any liquid used should be of an antifreeze typeso that itwill not freeze when exposed to the permafrost nor freeze in conduits 8and 14 should the system be shut down and exposed to ambient freezingconditions for prolonged periods. For example, alcohol, particularlyglycols such as ethylene glycol, can be used alone or in any combinationwith each other or with water (fresh or salt water).

The antifreeze material preferably has a freezing point of at least 60F. The antifreeze can be composed of from about 10 to about volumepercent water with the remainder being essentially one or more alcohols,and the like. Of course,

heated air or any other readily available heated gas can be employed ifdesired although better heat transfer results are achieved using aliquid heat exchange medium.

Well bore 1 is preferably lined with casing and the casing should beadapted to either prevent thawing of the permafrost in those areas ofthe well bore which are: heated by way of conduit 7, e.g., by insulatingthe casing and/or refrigerating the casing, or to accept some subsidenceof the permafrost such as r by the use of slip joints spacedperiodically along the length of the casing in at least part of thepermafrost zone.

Other heating means can be employed such as by the use of electricdownhole heaters and the like, so long as the gas passing throughconduit 6 is heated sufficiently that it is not cooled by exposure topermafrost zone: 4 to the point where substantial amounts of hydratewill form. Thus, substantially any heater means for heating at leastpart of conduit 6 over at least part of its length in the well bore canbe employed in combination with means for supplying energy to thatheater means.

According to the method of this invention the gas containing hydrateforming water and hydrocarbon is initially above the temperature andpressure at which substantial amounts of hydrate form. By initially" itis meant that gas as produced from formation 9 into the lower portion ofwell bore 1 adjacent end 6.

According to this method the substantially hydrate free gas is producedthrough well bore 1 in a first conducting zone 6 and the gas is heatedin the first conducting zone during at least a part of the length ofwell bore 1 in a controlled manner so that the gas in conducting zone 6is not cooled sufficiently while passing through permafrost zone 4 tocause substantial hydrate formation.

The hydrate itself is a complex combination of hydrocarbons and water.The chemical composition of the hydrate is presently unknown. Thehydrate is formed through the mechanism of water vapor in the gascondensing and freezing in a manner which ties hydrocarbon molecules inwith the frozen water. The hydrate is solid like ice but has asubstantial hydrocarbon content. The hydrate forms at temperatures above32 F. and can form at temperatures up to about 80 F. and higher in somesituations.

Any water present in the gas produced is a potential hydrate former sothat there is substantially no minimum amount of water in a hydrocarboncontaining gas below which the hydrate formation potential isnonexistent. Normally, the gas produced from a formation is saturatedwith water so that there normally is a very substantial potential forthe formation of large amounts of hydrate.

The formation of a hydrate and its pipe plugging propensities aresignificant in the production of gas wells through a permafrost zone.The problem of hydrate formation is not presently considered significantin the production of oil wells. This is so because there is a smalleramount of gas associated with the liquid oil and the liquid oil flowingthrough the conduits and pipes carries the hydrate out rather thanallowing the hydrate to build up in the piping as was discovered to bethe case with gas wells.

In an exemplary situation, the gas is, as initially produced, aboveabout 80- F. and above about 100 p.s.i.g. In this situation the hydratenormally forms in the gas at less than 80 F. and less than 10,000p.s.i.g. In this situation the gas in conduit 6 is heated to maintain atemperature of that gas greater than 80 F. while in permafrost zone 4.Of course, pressure plays some role in the determination at whichtemperature hydrate formation will occur. Generally. however, there is atemperature such as 80 F. for most natural gases, above whichsubstantially no hydrate will form at any practical pressure, i.e., lessthan about 10,000 p.s.i.g.

The heating of the gas in conducting zone 6 can be carried out in anypart of well bore 1 but is preferably carried out in at least part ofthe length of permafrost zone 4.

in the method of this invention the heating can be carried out in anymanner disclosed hereinabove with respect to the apparatus and thereforeincludes, inter alia, passing a heated fluid down the well bore in asecond conducting zone such as conduit 7, contacting the firstconducting zone 6 with the heated fluid, and raising the heated fluid atleast part way to the earth's surface while in contact with the firstconducting zone. The heated liquid is preferably raised while inconcentric contact with the interior or exterior or both of the firstconducting zone.

The heating can also be carried out by passing the heated liquid downthe well bore in the second conducting zone 7, the second conductingzone being substantially concentric with the interior and/or exterior ofthe first conducting zone 6 so that the heated liquid passes down thewell bore in contact with the first conducting zone 6 and is removedfrom the first conducting zone at the lower end of the second conductingzone for retrieval upward in the well bore to conduit 8.

EXAMPLE A natural gas well in northern Alaska was produced usingsubstantially the apparatus shown in the drawing. The permafrost zone 4was about 1,800 feet thick and the natural gas produced at the bottom ofthe production conduit 6 was at a temperature of about 175 F. and apressure of about 4,000 p.s.i.g. This gas contained about 170 pounds ofwater per million cubic feet of gas. The average temperature of wellbore 1 in permafrost zone 4 was l0 F. and hydrate formation started inthe gas when cooled to a temperature in the range of 75 to F.

Without employing the heating concept of this invention the natural gasremoved from conduit 6 at the earth 's surface was less than 75 F. andabout 3,000 p.s.i.g. at a flow rate of about 3 million cubic feet perday and contained sufficient solid hydrate that the three-inch insidediameter piping employed for carrying the natural gas to and throughadditional processing steps was readily plugged in a plurality of placesby a buildup of hydrate.

Employing the heating concept of this invention, a direct fired heater13 having a capacity of 4,000,000 B.t.u. per hour was utilized to heat amixture composed of 60 volume percent ethylene glycol and 40 volumepercent water to about l80 F. The heated glycol-water mixture was thenpumped downwardly through conduit 7 at a maximum rate of 75 gallons perminute, the interior casing diameter for the well bore in permafrostzone 4 being 20 inches. By following this procedure the natural gas inconduit 6 was maintained at a temperature greater than 80 F. as itpassed through permafrost zone 4 and no hydrate plugging problems wereencountered in piping the thus heated natural gas over the surface ofthe earth through various subsequent processing plants.

Reasonable variations and modifications are possible within the scope ofthis disclosure without departing from the spirit and scope of thisinvention.

We claim:

1. In a method of producing a gas well wherein gas is produced through awell bore which passes through a permafrost zone, said gas containinghydrate forming water and hydrocarbons but initially being at atemperature sufficiently elevated so that hydrate is not present, theimprovement comprising producing said gas through said well bore in afirst conducting zone, heating said gas while in said permafrost zone,said heating being conducted so that said gas'is not cooled sufficientlywhile passing through the permafrost zone of said well bore to cause theformation of substantial amounts of hydrate in said gas while in saidfirst conducting zone and so that thawing of the permafrost due to saidheating is substantially prevented.

2. A method according to claim 1 wherein said gas is saturated withwater as it enters said first conducting zone.

3. A method according to claim 1 wherein said gas is natural gas and isinitially above about 80 F. and p.s.i.g. hydrate forms in said gas atless than 80 F. and 10,000 p.s.i.g. and said gas is heated to maintain atemperature greater than 80 F. while in the permafrost zone of said wellbore.

4. A method according to claim 1 wherein said heating is carried out bypassing a heated liquid down said well bore in a second conducting zone,contacting said first conducting zone with said heated liquid, andraising said heated liquid at least part way to the earth's surfacewhile in contact with said first conducting zone.

5. A method according to claim 4 wherein said heated liquid is raisedwhile in concentric contact with at least one of the interior andexterior of said first conducting zone.

6. A method according to claim 1 wherein said heating is carried out bycontacting at least a portion of said first conducting zone in at leastpart of the length of said permafrost zone with a heated liquidantifreeze.

7. A method according to claim 6 wherein said antifreeze has a freezingpoint of at least 60 F.

8. A method according to claim 6 wherein said antifreeze is composed offrom abut 10 to about 90 volume percent water, the remainder beingessentially ethylene glycol.

9. A method for producing a gas well wherein natural gas is producedthrough a well bore which passes through a permafrost zone, said gascontaining hydrate forming water and hydrocarbons, said hydrate formingin said gas at less than 80 F. and 10,000 p.s.i.g., said gas initiallybeing above about 80 F. and 100 p.s.i.g., the steps comprising producingsaid gas through said well bore in a first conducting zone, passing aheated fluid down said well bore in a second conducting zone, contactingsaid first conducting zone with said heated fluid near the bottom ofsaid permafrost zone, raising said heated fluid at least part way to theearth's surface while in contact with said first conducting zone,controlling said heated fluid so that said gas is maintained at atemperature greater than F. while in said permafrost zone, andpreventing substantial thawing of the permafrost during passage of saidheated fluid through said conducting zones.

*3 l! l t 141

1. In a method for producing a gas well wherein gas is produced througha well bore which passes through a permafrost zone, said gas containinghydrate forming water and hydrocarbons but initially being at atemperature Sufficiently elevated so that hydrate is not present, theimprovement comprising producing said gas through said well bore in afirst conducting zone, heating said gas while in said permafrost zone,said heating being conducted so that said gas is not cooled sufficientlywhile passing through the permafrost zone of said well bore to cause theformation of substantial amounts of hydrate in said gas while in saidfirst conducting zone and so that thawing of the permafrost due to saidheating is substantially prevented.
 2. A method according to claim 1wherein said gas is saturated with water as it enters said firstconducting zone.
 3. A method according to claim 1 wherein said gas isnatural gas and is initially above about 80* F. and 100 p.s.i.g. hydrateforms in said gas at less than 80* F. and 10,000 p.s.i.g. and said gasis heated to maintain a temperature greater than 80* F. while in thepermafrost zone of said well bore.
 4. A method according to claim 1wherein said heating is carried out by passing a heated liquid down saidwell bore in a second conducting zone, contacting said first conductingzone with said heated liquid, and raising said heated liquid at leastpart way to the earth''s surface while in contact with said firstconducting zone.
 5. A method according to claim 4 wherein said heatedliquid is raised while in concentric contact with at least one of theinterior and exterior of said first conducting zone.
 6. A methodaccording to claim 1 wherein said heating is carried out by contactingat least a portion of said first conducting zone in at least part of thelength of said permafrost zone with a heated liquid antifreeze.
 7. Amethod according to claim 6 wherein said antifreeze has a freezing pointof at least -60* F.
 8. A method according to claim 6 wherein saidantifreeze is composed of from about 10 to about 90 volume percentwater, the remainder being essentially ethylene glycol.
 9. A method forproducing a gas well wherein natural gas is produced through a well borewhich passes through a permafrost zone, said gas containing hydrateforming water and hydrocarbons, said hydrate forming in said gas at lessthan 80* F. and 10,000 p.s.i.g., said gas initially being above about80* F. and 100 p.s.i.g., the steps comprising producing said gas throughsaid well bore in a first conducting zone, passing a heated fluid downsaid well bore in a second conducting zone, contacting said firstconducting zone with said heated fluid near the bottom of saidpermafrost zone, raising said heated fluid at least part way to theearth''s surface while in contact with said first conducting zone,controlling said heated fluid so that said gas is maintained at atemperature greater than 80* F. while in said permafrost zone, andpreventing substantial thawing of the permafrost during passage of saidheated fluid through said conducting zones.